Greywater 101

Learn how to safely reuse your household's wastewater and take water efficiency to the next level.

The average Australian home uses up to 44 per cent of household water on the garden in the hot summer months.

Credit: iStockphoto

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Think about all the times you turn on a tap at home each day: from splashing water on your face first thing in the morning to brushing your teeth before you go to sleep. It’s estimated each person in the average Australian household produces 120 L of so-called wastewater a day. And yet, of that, 84 L is greywater that could be reused to water the garden or flush the toilet. Tap into this resource to conserve drinking water, reduce the amount of pollution going into our waterways and save money on your water bills.

What is greywater?

On the most basic level, greywater is any water that leaves the house through a plughole. The name makes more sense in context; ‘whitewater’ comes from the tap, and ‘blackwater’ is what leaves the toilet.

Usually, greywater and blackwater leave the house through the same pipes en route to sewage treatment plants. The treated wastewater is discharged into oceans and rivers. The alternative is to reuse your greywater, radically reducing household water use as well as the total amount of effluent.

Some municipal councils use treated greywater and, in some cases, treated blackwater (also known as recycled water) to keep sports ovals and nature strips green and to flush public toilets.

It’s surprisingly cheap and easy to set up a simple greywater system in your home and garden.

What precautions should I take when using greywater?

Often greywater is warm when it’s collected; a perfect temperature for bacteria to breed in, so it should be assumed that all greywater contains bacteria. Greywater may also contain parasites or infectious viruses. For these reasons, never drink greywater or use it for cooking, even if it has been treated. In the garden, it’s best if greywater is applied below the surface of the garden bed (via a dripline on top of the soil, under mulch or in mulch-filled trenches) rather than sprayed. It’s also not advisable to use greywater on fruit or vegetables that you plan to eat raw.

Greywater from the kitchen can contain food particles that provide nutrients to help your plants grow, however, kitchen water isn’t usually recommended as it has lots of fats and food residue that can block plumbing or get smelly.

Bathroom greywater can contain soap and salts that are toxic to plants and tiny animals in the soil, so make sure you use only eco-friendly shampoos, soaps and body washes.

You’ll need to be careful with laundry detergents, as most powders and some liquids are sodium-based, and high sodium levels can inhibit seed growth. Choose laundry products that are low in phosphates and free from bleaches, bath salts, artificial dyes, cleansers, or boron (lots is toxic to plants).

It’s best to rotate where you use the greywater, as it’s thought that the long-term effects on soil can affect productivity.

Greywater reuse is becoming more and more common in households here and overseas and, if you follow these precautions, the associated risks are very low. Given that Australia is the driest inhabited continent on Earth, it makes sense to save drinking water for drinking, and to bring the mantra of reduce, reuse, recycle to our water consumption habits.

What ways are there to capture greywater?

There are two ways to capture greywater; collecting it before it goes down the plughole, or fixing new pipes
from the plugholes to a greywater storage tank.

If you’re renting or not sure you want to install a greywater system, go with a humble bucket in the shower and kitchen. Because clothes washing machines have a pump and the outlet is easy to access, everyone can consider a pipe extension from their laundry to the garden. Or, you could install a dual-purpose loo, which fills the cistern for the next flush with the water you use to wash your hands.

Installing a greywater system is the less labour-intensive option to carting buckets around the house. A simple greywater system from a single source costs as little as $200. Connecting greywater to your garden from multiple sources can be done for around $700 to $1,400, and if you want to install a comprehensive system for the whole house, expect to pay between $2,100 to $3,300. Some states in Australia require that greywater is delivered underground, so you’ll need to factor in the cost of an irrigation system.

You’ll also need to decide if you’re going to reuse the water with or without purifying or decontaminating it of all the soaps, salts and detergents. Water can be purified in a number of ways – using biological systems such as constructed wetlands, microbial digestion, or using UV radiation – but the easiest option for the urban home is filtration, mostly through sub-surface sand or by machine. A treatment system isn’t cheap, costing as much as $10,000 to buy and install.

What can greywater be used for around the home?

The average Australian home uses up to 44 per cent of household water on the garden over the hot summer months. Greywater is most commonly used untreated to water gardens via a sub-surface system directly to the roots of plants – that way there’s no human contact and it requires little maintenance.

A clearly marked, treated greywater tap in your backyard can be useful for occasional tasks such as washing the car, when you really don’t need to use fresh drinking water. Just remember to wash your hands with clean water afterwards, as there are higher levels of bacteria in greywater.

While some countries have banned the use of greywater indoors for purposes such as flushing the toilet and washing clothes, it is allowed in Australia, provided you have an appropriate treatment system.

How do I get started?

If you’re only installing from one or two sources, consider which ones will be the most beneficial. An estimated 58 per cent of household wastewater comes from the shower and handbasin, so if there’s easy access to the bathroom it makes sense to divert water from here first.

You also need to think about where you’ll be diverting your water. Do you want to divert greywater from the bathroom to a treatment system and then onto the laundry, or just from the laundry and shower into the garden? Bathrooms can be difficult places to set up a diversion because they’re often set on a concrete slab. Water sources from a second storey can work well because you can use gravity to help drain greywater into a tank, but be prepared to rip out parts of the ceiling to get access.

Don’t forget to check out any special requirements within your state or territory regarding the installation and use of greywater here. There’s also a range of state, territory and local government rebates available, however federal rebates were ditched earlier this year, so greywater systems installed after 10 May 2011 are no longer eligible.